(251e) Dynamics of DNA Release From Polyplexes Induced by Inter-Polyelectrolyte Exchange

Polymeric gene delivery vectors are attractive alternatives to viral carriers because of their lower safety risk, higher gene carrying capacity, and more targeting cell types. A major problem of polymeric gene carriers is their short circulation half-life. Polymeric gene delivery carriers are unstable in extracellular environment, which results in low transfection efficiency. We carried out a mechanistic study of DNA release by polyelectrolyte exchange using heparin and serum. The study was carried out at the single polyplex level using real-time atomic force microscopy (AFM) imaging. Bioreducible hyperbranched poly(amido amine)s (PAA)s and modified bioreducible PAAs were studied. The AFM results are correlated with fluorescence data as well as cell transfection data.  A critical heparin concentration above which significant DNA release occurs was determined. The critical concentration was found to be a function of polycation charge density, chain architecture, and amine to phosphate (N/P) ratio. AFM captured morphological release pathway with distinct polyplex structures. These characteristic morphologies include core-shell, toroid, nanoparticle decorated toroid, and loose chains held by a compact core structure. In addition, PEG and hyaluronic acid modification were shown to be effective against inter-polyelectrolyte exchange and improve gene delivery efficiency. This study contributes to basic understanding of DNA release dynamics from single polyplex particles in simulated physiologic conditions and provides synthetic strategies to improve gene delivery efficiency of polymeric vectors.